Method for sending RLC PDU and allocating radio resource in mobile communications system and RLC entity of mobile communications

ABSTRACT

Disclosed is a transmission of a RLC STATUS PDU using a limited radio resource by MAC and RLC layers in a long term evolution (LTE) system. In case where the MAC entity prioritizes logical channels for allocating the radio resource to each logical channel, the MAC entity is allowed to allocate radio resources based upon the size of a RLC STATUS PDU to be sent from the RLC layer and also the RLC layer is allowed to use the STATUS PDU prior to RLC data PDUs upon using the allocated radio resource, such that RLC protocols can be avoided from coming in a deadlock situation due to a non-transmission of the STATUS PDU.

The present application claims the priority benefits of U.S. ProvisionalApplications Nos. 61/025,311 and 61/026,119 respectively filed on Feb.1, 2008 and Feb. 4, 2008 and Korean Patent Application No.10-2009-0007152 filed on Jan. 29, 2009 in Republic of Korea. The entirecontents of these applications are herein fully incorporated byreference.

TECHNICAL FIELD

The present invention relates to a radio protocol in a mobilecommunications system, and more particularly, a method in which MAC andRLC layers in a long term evolution (LTE) system sends RLC STATUS PDUsusing a limited radio resource.

BACKGROUND ART

FIG. 1 is a network architecture of a long term evolution (LTE) systemwhich is the related art mobile communication system has evolved fromthe existent UMTS system and a basic standardization therefor isundergoing in 3GPP.

The LTE network may be divided into evolved UMTS terrestrial radioaccess network (E-UTRAN) and core network (CN). The E-UTRAN includes aterminal (User Equipment; UE), a base station (Evolved Node B; eNB), anaccess gateway (aGW) located at the end of the network to be connectedto an external network. The aGW may be divided into a portion ofhandling a user traffic and a portion of processing a control traffic.Here, a new interface may be used for the communication between the aGWfor processing the user traffic and the aGW for processing the controltraffic. One or more cells may exist in one eNB. An interface fortransmission of the user traffic or control traffic may be used betweeneNBs. The CN may include an aGW, a node for a user registration of otherUEs and the like. An interface may be used to identify the E-UTRAN andCN.

FIG. 2 is an architecture of a radio interface protocol control planebetween a terminal and an E-UTRAN based upon the 3GPP radio accessnetwork standard, and FIG. 3 is an architecture of a radio interfaceprotocol user plane between a terminal and an E-UTRAN based upon the3GPP radio access network standard.

Hereinafter, the architecture of radio interface protocols between theterminal and the E-UTRAN will be described with reference to FIGS. 2 and3.

The radio interface protocol has horizontal layers comprising a physicallayer, a data link layer and a network layer, and has vertical planescomprising a user plane for transmitting data information and a controlplane for transmitting a control signaling. The protocol layers can bedivided into a first layer (L1), a second layer (L2) and a third layer(L3) based on three lower layers of an Open System Interconnection (OSI)standard model widely known in communications systems. Such radiointerface protocols may exist as a pair between the terminal and theE-UTRAN, to manage data transmissions over interfaces.

Hereinafter, each layer in the radio protocol control plane in FIG. 2and the radio protocol user plane in FIG. 3 will be described.

A first layer, as a physical (PHY) layer, provides an informationtransfer service to an upper layer using a physical channel. Thephysical layer is connected to its upper layer, called a Medium AccessControl (MAC) layer, via a transport channel. The MAC layer and thephysical layer exchange data via the transport channel. Here, thetransport channels may be divided into a dedicated transport channel anda common transport channel depending on whether the transport channel isshared. Data is transferred via a physical channel between differentphysical layers, namely, between the physical layer of a transmittingside and the physical layer of a receiving side.

Various layers exist in the second layer. First, a medium access control(MAC) layer serves to map different logical channels to differenttransport channels, and also performs a logical channel multiplexing formapping several logical channels to one transport channel. The MAC layeris connected to an upper radio link control (RLC) layer via a logicalchannel. Logical channels are is divided according to a type ofinformation to be transmitted into a control channel for transmittingcontrol plane information and a traffic channel for transmitting userplane information.

The RLC layer of the second layer manages segmentation and concatenationof data received from an upper layer to appropriately adjust a data sizesuch that a lower layer can send data over an interface. Also, the RLClayer provides three operation modes, including a transparent mode (TM),an un-acknowledged mode (UM) and an acknowledged mode (AM), so as toguarantee various quality of service (QoS) requirements of each radiobearer (RB). In particular, the RLC layer operating in the AM mode(hereinafter, referred to as AM RLC layer) performs a retransmissionusing an automatic repeat and request (ARQ) function for a reliable datatransmission.

A packet data convergence protocol (PDCP) layer located at the secondlayer is used to efficiently transmit IP packets, such as IPv4 or IPv6,on a radio interface with a relatively small bandwidth. For thispurpose, the PDCP layer reduces the size of an IP packet header which isrelatively great in size and includes unnecessary control information,namely, performs a function called header compression. Accordingly, onlynecessary information can be included in the header part of data fortransmission, so as to increase a transmission efficiency of a radiointerface.

A radio resource control (RRC) layer located at the lowermost portion ofthe third layer is only defined in the control plane. The RRC layercontrols logical channels, transport channels and physical channels inrelation to configuration, re-configuration and release of Radio Bearers(RBs). Here, the RB denotes a logical path that the L2 layer providesfor data transmission between the terminal and the UTRAN. In general,the establishment of the RB refers to stipulating the characteristics ofprotocol layer and channel required for providing a specific service,and setting the respective detailed parameters and operation methods.The RBs are divided into a signaling RB (SRB) and a data RB (DRB). TheSRB is used as a path for transmission of RRC messages in the C-plane,while the DRB is used as a path for transmissions of user data in theU-plane.

Hereinafter, the RLC layer will be described in more detail. The RLClayer provides three modes, such as the TM, UM and AM, as mentionedabove. The RLC layer rarely performs a function in the TM, and thus UMand AM will only be described herein. The UM RLC adds a protocol dataunit (PDU) header including a sequence number (SN) to each PDU fortransmission, such that a receiving side can be known as to which PDUhas been lost during transmission. Due to such function, the UM RLCmanages, in the user plane, the transmission of multimedia data or thetransmission of real-time packet data, such as voice (e.g., VoIP) orstreaming in a packet service domain (hereinafter, referred to as a PSdomain), while managing, in the control plane, the transmission of anRRC message, which does not need a reception acknowledgement, among RRCmessages sent to a specific terminal or specific terminal group within acell.

Similarly, the AM RLC constructs a PDU by adding a PDU header includingan SN upon the construction of PDU. Unlike the UM RLC, a receiving sideacknowledges a PDU sent by a transmitting side. The receiving sideacknowledges in order to request a retransmission of unsuccessfullyreceived PDU from the transmitting side. Such retransmission function isthe most important characteristic of the AM RLC. Thus, the AM RLC aimsto guarantee an error-free data transmission via the retransmission.Under the purpose, the AM RLC usually manages a non-real-time packetdata transmission, such as TCP/IP of PS domain, in the user plane, whilemanaging a transmission of RRC message, which requires a receptionacknowledgement, among RRC messages transmitted to a specific terminalwithin a cell in the control plane.

From the perspective of direction, the UM RLC is used for aunidirectional communication, while the AM RLC is used for abi-directional communication due to a feedback from a receiving side.From the structural perspective, there is a difference, namely, the UMRLC is configured such that one RLC entity performs transmission orreception while the AM RLC is configured such that both transmittingside and receiving side exist in one RLC entity. The complicatedconfiguration of the AM RLC is due to the retransmission. The AM RLCincludes a retransmission buffer for managing the retransmission, inaddition to a transmission/reception buffer. Also, the AM RLC performsvarious functions, such as using transmitting and receiving windows fora flow control, polling for a transmitting side to request statusinformation from a receiving side of an RLC entity, sending a statusreport for a receiving side to report its buffer state to a transmittingside of a peer RLC entity, constructing a status PDU for deliveringstatus information, and the like. The AM RLC also needs various protocolparameters, such as status variables and a timer, in order to supportthe functions. A PDU, such as status report or status PDU, which is usedfor controlling the data transmission in the AM RLC, is referred to as‘Control PDU’, and a PDU used for transferring user data is referred toas ‘Data PDU’.

An RLC data PDU in the AM RLC may be divided into AMD PDU and AMD PDUsegment, in detail. The AMD PDU segment has part of data included in theAMD PDU. In the LTE system, a maximum size of a data block is changeableevery time a terminal sends the data block. Hence, after a transmittingside AM RLC entity constructs a 200-byte AMD PDU at a specific time andtransmits the constructed AMD PDU, when the transmitting side AM RLCreceives NACK from a receiving side AM RLC and thereby tries toretransmit the AMD PDU, if a maximum size of data block to be actuallytransmittable is 100 bytes, the same AMD PDU cannot be sent as it is. Inthis case, the AMD PDU segment is used. The AMD PDU segment denotes thatthe corresponding AMD PDU is segmented into smaller units. During theprocedure, the transmitting side AM RLC entity divides the AMD PDU intothe AMD PDU segments and transmits the AMD PDU segments over severaltransmission time intervals. The receiving side AM RLC entity thenrestores the AMD PDU from the received AMD PDU segments.

If there is unsuccessfully (incompletely or incorrectly) received data,the receiving side AM RLC requests a retransmission of such data fromthe transmitting side AM RLC, which is referred to as ‘status report’.The status report is sent by using STATUS PDU, which is one of controlPDUs.

FIG. 4 is a format of STATUS PDU currently used in the LTE system. InFIG. 4, a horizontal axis denotes a length of an RLC STATUS PDU with 8bits, namely, 1 octet.

Each field of the RLC STATUS PDU will now be described.

1. Data/Control (D/C) field: 1 bit

-   -   This field indicates whether a corresponding RLC PDU is either        RLC data PDU or RLC control PDU.

2. Control PDU type (CPT) field: 3 bits

-   -   This field indicates what type a corresponding control PDU is.        The RLC control PDU currently defines only the STATUS PDU.

3. Acknowledgement Sequence Number (ACK_SN)

-   -   Two types of ACK_SN will be defined as follows.        -   1-1) A type of ACK_SN is an RLC SN of a first PDU whose            information is not included in a STATUS PDU.        -   1-2) Upon receiving the STATUS PDU, a transmitting side            determines that all the PDUs among PDUs up to the PDU with            ACK_SN-1 have successfully been received by a receiving            side, excluding PDUs indicated in the STATUS PDU with NAC_SN            or portions of PDUs indicated in the STATUS PDU with            NACK_SN, SOstart and SOend.

Such ACK_SN was applied to embodiments of FIGS. 6 and 8 according to thepresent invention.

2-1) Another type of ACK_SN is an RLC SN of a first PDU whoseinformation is included in a STATUS PDU.

2-2) Upon receiving the STATUS PDU, the transmitting side determinesthat all the PDUs among PDUs up to the PDU with the ACK_SN havesuccessfully been by the receiving side, excluding PDUs indicated in theSTATUS PDU with NACK_SN or portions of PDUs indicated in the STATUS PDUwith NACK_SN, SOstart and SOend.

Such ACK_SN was applied to embodiments of FIGS. 7 and 9 according to thepresent invention.

4. Extension 1 (E1): 1 bit

This indicates whether there is another NACK_SN element following acurrent NACK_SN element (i.e., indicated with NACK_SN or with NACK_SN,SOstart and SOend).

5. NACK_SN (Negative acknowledgement Sequence Number)

This is an RLC SN of an unsuccessfully received AMD PDU or AMD PDUsegment.

5. Extension 2 (E2): 1 bit

This indicates whether there are SOstart and SOend fields correspondingto a current NACK_SN.

6. Segment Offset Start (SOstart) and Segment Offset End (SOend)

These are used when only a part (segment) of PDU with NACK_SN is NACK. Afirst byte of the part corresponds to the SOstart and the last bytethereof corresponds to the SOend.

In the meantime, the receiving side AM RLC cannot always trigger aSTATUS PDU, but can trigger a status reporting only when a specificcondition is met. Such condition is referred to as ‘status reportingtrigger’, and the LTE system currently uses two conditions as follows.

The first condition is a polling of a transmitting side.

That is, when desiring to receive a status report from a receiving side,the transmitting side AM RLC sets a poll bit for an RLC data PDU fortransmission.

The receiving side AM RLC then triggers the status report upon receivingthe poll bit set RLC data PDU.

The second condition is a detection of an unsuccessful reception of RLCdata PDU.

That is, upon detecting an unsuccessfully received RLC data PDU (i.e.,AMD PDU or AMD PDU segment) after completing a HARQ reordering, thereceiving side AM RLC triggers the status report.

In addition, when the status report is triggered, the receiving side AMRLC sends a reception buffer state to the transmitting side using aSTATUS PDU. Here, is the STATUS PDU includes information up to the lastPDU (=VR(MS)) among PDUs within the range of a PDU (=VR(R)) with a startpoint of a receiving window to a HARQ reordering completed PDU. Here,the VR(R) and VR(MS) denote state variables, which are managed by thereceiving side AM RLC and used for a receiving window, a status reportand the like. Among others, the receiving AM RLC manages additionalstate variables.

Such additional state variables of the receiving side AM RLC aredescribed as follows.

-   -   VR(R): Receive state variable.        -   It hold a value of a sequence number (SN) of an AMD PDU            subsequent to the last AMD PDU among AMD PDUs received            in-sequence.        -   It is a first AMD PDU among AMD PDUs which are not            completely (successfully) received by the receiving side AM            RLC.        -   It serves as the lower edge of the receiving window.        -   It is initially set to 0. When completely receiving an AMD            PDU with SN=VR(R), it is updated to a value of SN of a first            incompletely received AMD PDU subsequent to the AMD PDU.    -   VR(MR): Maximum acceptable receive state variable.        -   It holds a value of SN of the first AMD PDU among AMD PDUs            outside a receiving window.        -   It serves as the higher edge of the receiving window.        -   It is updated, for example, to VR(MR)=VR(R)+AM_Window_size            when the VR(R) is updated.    -   VR(X): T_reordering state variable        -   It holds a value of SN of an RLC data PDU subsequent to an            RLC data PDU which triggered a T_reordering as a timer for            managing a HARQ reordering.        -   A receiving side AM RLC drives the T_reordering upon            receiving an out-of-sequence RLC data PDU under a condition            that no T_reordering is triggered, and sets the VR(X) to the            value of SN of an RLC data PDU subsequent to the RLC data            PDU.    -   VR(MS): Maximum status transmit state variable        -   This state variable is used for including in a STATUS PDU            information only related to RLC data PDUs for which the HARQ            reordering is completed.        -   It is initially set to 0, and upon completely receiving an            AMD PDU with SN=VR(MS), it is updated to a value of SN of a            first incompletely received AMD PDU following the AMD PDU.    -   Upon the T_reordering expired, it is updated to a value of SN of        a first incompletely received AMD PDU among AMD PDUs higher than        VR(X). ACK_SN is set to the VR(MS) so as to construct a STATUS        PDU.    -   VR(H): highest received state variable        -   It holds a value of the very next SN of the highest SN among            RLC data PDUs received by the receiving side AM RLC, namely,            a value of SN of an RLC data PDU which is first            unsuccessfully received by the receiving side AM RLC.        -   It is initially set to 0, and upon receiving an RLC data PDU            higher than VR(H), it is updated to a value of SN of an RLC            data PDU subsequent to the RLC data PDU.

Hereinafter, a logical channel prioritization (LCP) performed by the MAClayer will be described.

When several radio bearers (RBs) are multiplexed and transmitted overone transport channel, an LTE terminal is configured such that its MAClayer decides an amount of transmission data for each RB, based upon thefollowing rules, with respect to a given radio resource, for everytransmission time interval (TTI).

-   -   1. The MAC layer decides an amount of transmission data for        multiplexed RBs in a decreasing order of each logical channel        priority (LCP), and then decides a transmission amount as much        as data corresponding to a maximum prioritized bit rate (PBR)        for each RB.    -   2. If any radio resources remain, the MAC layer decides the        amount of transmission data for the multiplexed RBs in the        decreasing order of each LCP.

Here, 1 to 8 LCPs are currently discussed, and 1 denotes the highestpriority and 8 denotes the lowest priority. PBR denotes a minimum bitrate guaranteed for a corresponding RB, which means that the LTE systemcan support such degree of bit rate even under a very bad radioenvironment. The PBR may be set within the range of 0 to infinity.

In the meantime, LCP and PBR of each RB are sent from a network RRC to aterminal RRC via an RB setup message upon initially setting the RB.After receiving the RB setup message, the terminal RRC then setsnecessary RBs and sends information on LCP and PBR of each RB to aterminal MAC. The MAC having received such information decides atransmission amount of each RB with respect to a given radio resourcefor every TTI, base upon such rules.

DISCLOSURE Technical Solution

While performing a logical channel prioritization (LCP), the MACconsiders only LCP and PBR. Therefore, it is possible that, for acertain logical channel, the allocated radio resource might be smallerthan an RLC STATUS PDU to be sent via the corresponding logical channel.However, when a status report is triggered, a receiving side AM RLC isallowed to include all information related to AMD PDUs within a presetrange into a STATUS PDU for transmission. Accordingly, if the radioresource to send the STATUS PDU is smaller than the STATUS PDU, theconstructed STATUS PDU cannot be sent. The related art didn't considersuch situation. As a result, such situation occurs, the constructed RLCSTATUS PDU cannot be sent, thereby causing a deadlock situation.

Therefore, an object of the present invention is that, in case where aMAC layer performs a logical channel prioritization in order to allocatea radio resource to each logical channel, a MAC layer (MAC entity) isallowed to allocate a radio resource based upon the size of a RLC STATUSPDU to be sent from an RLC layer and the RLC layer is allowed to use aSTATUS PDU prior to RLC data PDU upon using the allocated radioresource, whereby RLC protocols can be prevented from coming in adeadlock due to an unsuccessful transmission of the STATUS to PDU. Tothis end, the present invention proposes the operation of the MAC andthe operation of the RLC, respectively.

To solve the problem of the related art, a method for transmitting radiolink control (RLC) protocol data units (PDUs) in a mobile communicationssystem, comprising: receiving an indication of available resource from amedium access control (MAC) entity; prioritizing transmission of RLCcontrol PDUs over RLC data PDUs using the indication of availableresource; and transmitting the prioritized RLC PDUs using the receivedavailable resource.

The method may further include allocating the available resource to theRLC control PDUs, and if any resource remains, then allocating theremaining resource to the RLC data PDUs.

The RLC control PDUs may denote RLC STATUS PDUs, and the method mayfurther include if the available resource indicated from the MAC entityis smaller than the size of one status PDU, skipping by the RLC entitythe transmission of one status PDU for this transmitting opportunity.

The available resource and the one status PDU may be checked for everytransmission time interval (TTI).

The RLC control PDUs may denote RLC STATUS PDUs, and the method mayfurther include checking by the RLC entity for every transmission timeinterval (TTI) whether a STATUS PDU is scheduled for transmission, andif so, then informing the size of the STATUS PDU to the MAC entity.

In one aspect of the present invention, a method for allocatingresources for transmission in a mobile communications system, mayinclude: allocating the resources such that all logical channels areserved in a decreasing priority order up to the size of each radio linkcontrol (RLC) STATUS protocol data unit (PDU) waiting for transmission;if any resources remain, allocating such remaining resources such thatall the logical channels are served in a decreasing priority order up totheir configured prioritized bit rate (PBR); and if any resourcesremain, allocating such remaining resources such that all the logicalchannels are served in a strictly decreasing priority order.

The method may further include: checking by a medium access control(MAC) entity whether a STATUS PDU is scheduled for transmission forevery transmission time interval (TTI) in the RLC entity; and receivinginformation related to the size of the STATUS PDU if there is the STATUSPDU scheduled for transmission.

In another aspect of the present invention, a method for allocatingresources in a mobile communications system, may include: allocating, bya medium access control (MAC) layer, resources such that all logicalchannels are served in a decreasing priority order up to eachprioritized bit rate (PBR) of the logical channels plus the size of eachRLC STATUS PDU waiting for transmission; and if any resources remain,allocating, by the MAC entity, the remaining resource such that all thelogical channels are served in a strict decreasing priority order.

The method may further include checking, by the MAC entity, whether aSTATUS PDU is scheduled for transmission for every TTI in the RLCentity, and receiving information related to the size of the STATUS PDUif the STATUS PDU is scheduled for transmission.

In one aspect of the present invention, a radio link control (RLC)entity in a mobile communications system may include a module configuredto: receive an indication of resource from a medium access control (MAC)entity; check whether there is a STATUS PDU is scheduled to be sent to apeer RLC entity; compare the size of the indicated resource with thesize of the STATUS PDU to be sent; primarily allocate the resource tothe STATUS PDU so as to send the STATUS PDU to the peer RLC entity ifthe resource is larger than or equal to the STATUS PDU according to thecomparison result; and skip the transmission of the STATUS PDU if theresource is smaller than the STATUS PDU according to the comparisonresult.

Advantageous Effect

The related art has not defined an operation method of a receiving sideAM RLC when a radio resource is smaller than a STATUS PDU scheduled fortransmission, which causes a deadlock situation of protocols. Therefore,the present invention allows a MAC layer to consider the size of a RLCSTATUS PDU upon allocating resources and also allows an RLC layer toprimarily allocate resources to a RLC STATUS PDU upon allocatingresources, so as to enable a stable operation of protocols regardless ofradio circumstances.

MODE FOR INVENTION

The present invention is applied to a mobile communication system, andparticularly, to an evolved universal mobile telecommunications system(E-UMTS) evolved from the UMTS. However, the present invention may notbe limited to the system, but applicable to any communication system andcommunication protocol complying with the scope of the presentinvention.

As the present features may be embodied in several forms withoutdeparting from the characteristics thereof it should also be understoodthat the above-described embodiments are not limited by any of thedetails of the foregoing description, unless otherwise specified, butrather should be construed broadly within its scope as defined in theappended claims, and therefore all changes and modifications that fallwithin the metes and bounds of the claims, or equivalents of such metesand bounds are therefore intended to be embraced by the appended claims.

Terms containing ordinal numbers such as 1, 2 and the like, may be usedto describe various components, but the components may not be limited tothe terms. The terms are used for the purpose of distinguishing onecomponent from another component. For example, a first component may benamed as a second component without departing from the scope of thepresent invention, and similarly the second component may be named asthe first component. A term ‘and/or’ will include a combination ofplural associated items or any of plural associated items.

When mentioning that one component is ‘connected’ or ‘accessed’ toanother component, the one component may be directly connected oraccessed to the another component, however, any intermediatecomponent(s) may exists therebetween. On the other hand, when mentioningthat one component is ‘directly connected’ or ‘directly accessed’ toanother component, it could be understood that other intermediatecomponents do not exist therebetween.

Terms used in the present invention are used to illustrate the preferredembodiments, but not intended to limit the present invention. A singularrepresentation may include a plural representation as far as itrepresents a definitely different meaning from the context. Terms‘include’ or ‘has’ used in the present invention should be understoodthat they are intended to indicate an existence of feature, number,step, operation, component, item or any combination thereof, disclosedin the specification, but should not be understood that they areintended to previously exclude an existence of one or more otherfeatures, numbers, steps, operations, components, or any combinationthereof or possibility of adding those things. As far as not beingdefined differently, all terms used herein including technical orscientific terms may have the same meaning as those generally understoodby an ordinary person skilled in the art to which the present isinvention belongs to. Commonly used terms having the same meaningsdefined in the dictionary should be construed as having the meaningsequal to the contextual meanings. As far as not being definitely definedin the present invention, such terms should not be construed as havingideal or excessively formal meanings.

Hereinafter, description will be given in detail of the preferredembodiments according to the present invention with reference to theaccompanying drawings. For the sake of brief description with referenceto the drawings, the same or equivalent components regardless ofreference numerals will be provided with the same reference numbers, anddescription thereof will not be repeated.

The present invention recognized the point that, for a certain logicalchannel, a STATUS PDU cannot be constructed if the allocated radioresource is smaller than a RLC STATUS PDU to be sent via thecorresponding logical channel.

Considering such recognition, the present invention is conceptuallycharacterized in that 1) in case where a MAC layer (MAC entity) performsa logical channel prioritization in order to allocate a radio resourceto each logical channel, 2) the MAC layer is allowed to allocate theradio resource based upon the size of a RLC STATUS PDU to be sent fromthe RLC layer, and also 3) the RLC layer is allowed to use the STATUSPDU prior to RLC data PDU upon using the allocated radio resource,whereby 4) the RLC protocols can be prevented from coming in a deadlocksituation due to a non-transmission of the STATUS PDU.

First and second embodiments of the present invention illustrate anoperation method in a MAC layer, and a third embodiment of the presentinvention illustrates an operation method in an RLC layer. In theembodiments of the present invention, a radio resource may briefly bereferred to as ‘resource’, and also is referred to as ‘transmittingresource’ because it is used for the transmission of a STATUS PDU.

Also, in the first to third embodiments of the present invention, theSTATUS PDU is sent from an RLC entity to a peer RLC entity. Thus, theSTATUS PDU may denote an RLC STATUS PDU, and the two names, STATUS PDUand RLC STATUS PDU, are all used in the description of the presentinvention.

Hereinafter, the first embodiment of the present invention is described.

When performing a logical channel prioritization (LCP) procedure, a MAClayer primarily considers, for each logical channel, the size of aSTATUS PDU constructed by an RLC. That is, upon performing the LCPprocedure, the MAC layer first considers the size of RLC STATUS PDU ofeach logical channel in a decreasing priority order of each logicalchannel so as to allocate radio resources, and thereafter performs therelated art LCP procedure.

The first embodiment of such procedure is described with reference toFIG. 5.

FIG. 5 is a flowchart illustrating a logical channel prioritization(LCP) of a MAC layer in accordance with a first embodiment of thepresent invention. The LCP procedure of FIG. 5 is performed for everyTTI.

Referring to FIG. 5, a MAC layer (or MAC entity) receives informationrelated to the size of a RLC STATUS PDU (RLC STATUS PDU sizeinformation) from each RLC entity (S1). The MAC layer considers the RLCSTATUS PDU size information received from each RLC entity so as toallocate radio resources to each logical channel in the decreasing orderof each logical channel priority (S2).

If any radio resources remains (S3) after the allocation of radioresource to each logical channel at the step S2, then the remainingradio resource is allocated to each logical channel in the decreasingpriority order up to their configured PBR (S4). After the step S4, ifany radio resource remains, the remaining radio resource is allocated todata in the decreasing priority order (S6).

FIG. 6 is a flowchart illustrating a logical channel prioritization(LCP) procedure of a MAC layer in accordance with a second embodiment ofthe present invention, which is another exemplary embodiment of the LCPprocedure of the MAC layer. The LCP procedure of FIG. 6 is performed forevery TTI. Comparing the second embodiment of FIG. 6 with the firstembodiment of FIG. 5, in the embodiment of FIG. 6, upon allocatinglogical channels, the LCP procedure is performed based upon each STATUSPDU size and each PBR. That is, all the logical channels are allocatedbased upon each PBR and each RLC STATUS PDU in the decreasing order ofthe logical channel priority.

Hereinafter, the LCP procedure according to the second embodiment of thepresent invention will be described in more detail with reference toFIG. 6.

The MAC layer (MAC entity) receives information related to the size ofRLC STATUS PDU (RLC STATUS PDU size information) from each RLC entity(S11). The MAC layer then allocates radio resources to each logicalchannel in a decreasing priority order based upon the RLC STATUS PDUsize information received from each RLC entity and each PBR (S12).

After the step S12, if any radio resource remains (S13), the MAC layermay further allocate the remaining resource to data in the decreasingpriority order (S14).

In the meantime, in case of the first and second embodiments of thepresent invention, for each TTI, in order to consider the size of theRLC STATUS PDU of each logical channel during the LCP procedure, the RLCentity should inform the MAC layer of the size of the STATUS PDUscheduled for transmission.

As aforesaid, the first and second embodiments of the present inventionillustrate that radio resources can be allocated to each logical channelbased upon the RLC STATUS PDU size information, through the interactionbetween the RLC entity and the MAC layer. Therefore, in the presentinvention, the radio resources can be allocated to the STATUS PDU priorto data PDUs, such that the STATUS PDU can be sent prior to the dataPDUs.

Hereinafter, a third embodiment of the present invention will bedescribed.

FIG. 7 is a flowchart illustrating a method for allocating radioresources based upon a size of STATUS PDU, performed by an RLC layer, inaccordance with a third embodiment of the present invention.

For supporting the operation of the MAC, as illustrated in the first andsecond embodiments of the present invention, it should be checked foreach TTI whether a STATUS PDU scheduled for transmission exists, and ifso, the size of the corresponding STATUS PDU should be informed to theMAC. Such RLC-MAC interaction is required to allow the operation methodof the MAC.

However, unlike the above method, the RLC itself can be operated toavoid an RLC deadlock state. That is, when receiving information(indication) related to an available resource from the MAC layer, if theavailable resource is larger than or equal to the size of a STATUS PDU,the RLC entity may prioritize the STATUS PDU over RLC data PDUs fortransmission. That is, the available resource is first allocated to theRLC STATUS PDU, and if any resource remains, such remaining resource isallocated to the RLC data PDUs.

Also, if the available resource indicated from the MAC is smaller thanthe STATUS PDU, the RLC entity may not send the STATUS PDU (i.e., skipthe transmission of the STATUS PDU) for this transmitting opportunity.In other words, the RLC entity may send the STATUS PDU in the earliesttransmitting opportunity, namely, when the available resource is largerthan or equal to the size of the STATUS PDU.

Still referring to FIG. 7, the RLC entity receives an indication of anavailable resource from the MAC layer (S21). If the size of the receivedavailable resource is larger than or equal to the size of the STATUS PDU(S22), the RLC entity primarily allocates the resource to the RLC STATUSPDU (S23). After allocating the resource to the STATUS PDU, if anyresource remains, the RLC entity then allocates the remaining resourceto the RLC data PDU (S24). However, if the size of the radio resource issmaller than the size of the STATUS PDU (S22), the RLC entity skips thetransmission of the RLC STATUS PDU for this transmitting opportunity.Afterwards, the RLC entity checks the size of radio resource for everyTTI, so as to send the STATUS PDU when the size of the resource islarger than the STATUS PDU (S25).

Hereinafter, an RLC entity according to the present invention will bedescribed.

An RLC entity according to the present invention may be a deviceincluding a module configured to receive an indication of radio resourcefrom a MAC layer, check whether a STATUS PDU is scheduled to be sent toa peer RLC entity; compare the size of the received radio resource withthe size of the STATUS PDU scheduled for transmission, primarilyallocate the radio resource to the STATUS PDU so as to send the STATUSPDU to the peer RLC entity if the radio resource is larger than or equalto the STATUS PDU according to the comparison result, and skip thetransmission of the STATUS PDU if the radio resource is smaller than theSTATUS PDU according to the comparison result. In the meantime, themodule may include a plurality of components according to its function.That is, the module may include a receiving unit for receiving radioresource, a comparing unit for comparing the size of the radio resourcewith the size of the STATUS PDU scheduled for transmission, and atransmitting unit for transmitting the STATUS PDU. Therefore, the modulemay be implemented in various types of components each capable ofperforming its function.

The RLC entity according to the present invention basically includes, inaddition to the aforesaid component, software and hardware required forimplementing the scope of the present invention, for example, an outputdevice (e.g., display, speaker and the like), an input device (e.g.,keypad, microphone and the like), a memory, a transceiver (e.g., RFmodule, antenna and the like). Such components can be obviouslyunderstood by those skilled in the art, and thus a detailed descriptionthereof will not be repeated.

Meanwhile, the method according to the present invention, as describedso far, can be implemented by hardware or software, or any combinationthereof. For example, the method according to the present invention maybe stored in a storage medium (e.g., an internal memory of a mobileterminal, a flash memory, a hard disc, etc.). Alternatively, the methodaccording to the present invention can be implemented as codes orcommand words within a software program capable of being executed by aprocessor (e.g., a microprocessor in a mobile terminal).

The present invention has been explained with reference to theembodiments which are merely exemplary. It will be apparent to thoseskilled in the art that various modifications and equivalent otherembodiments can be made in the present invention without departing fromthe spirit or scope of the invention. Also, it will be understood thatthe present invention can be implemented by selectively combining theaforementioned embodiment(s) entirely or partially. Thus, it is intendedthat the present invention cover modifications and variations of thisinvention provided they come within the scope of the appended claims andtheir equivalents.

Description Of Drawings

FIG. 1 is a network architecture of a long term a long term evolution(LTE) system which is the related art mobile communication system;

FIG. 2 is an architecture of a radio interface protocol control planebetween a terminal and an E-UTRAN based upon the 3GPP radio accessnetwork standard;

FIG. 3 is an architecture of a radio interface protocol user planebetween a terminal and an E-UTRAN based upon the 3GPP radio accessnetwork standard;

FIG. 4 is a format of STATUS PDU currently used in the LTE system; toFIG. 5 is a flowchart illustrating a logical channel prioritizationprocedure of a MAC layer in accordance with a first embodiment of thepresent invention;

FIG. 6 is a flowchart illustrating a logical channel prioritizationprocedure of a MAC layer in accordance with a second embodiment of thepresent invention; and

FIG. 7 is a flowchart illustrating a method for allocating radioresources by considering a size of a STAUS PDU, performed by an RLClayer, in accordance with a third embodiment of the present invention.

The invention claimed is:
 1. A method for transmitting radio linkcontrol (RLC) STATUS protocol data units (PDUs) in a mobilecommunications system, the method comprising: receiving, by an RLCentity, an indication of a total size of an RLC PDU from a medium accesscontrol (MAC) entity; prioritizing, by the RLC entity, a transmission ofthe RLC STATUS PDUs over RLC data PDUs; constructing the prioritized RLCSTATUS PDUs including a data/control (D/C) field, a CTP field, an ACK_SNfield, and at least one NACK_SN field in order, the ACK_SN fieldincluding current information that is not received; and transmitting, bythe RLC entity, the constructed RLC STATUS PDUs associated with theindicated total size of the RLC PDU corresponding to a size of the RLCSTATUS PDUs to a peer RLC entity, wherein the constructed andtransmitted RLC STATUS PDUs include only negative acknowledgementinformation of RLC PDUs, and wherein the ACK_SN field is for the peerRLC entity to indicate previous information that is received.
 2. Themethod of claim 1, further comprising: performing a first step ofallocating an available resource to the RLC STATUS PDUs by the RLCentity; and if any of the available resource remains after the firststep of allocating, then performing a second step of allocating theremaining resource to the RLC data PDUs by the RLC entity.
 3. The methodof claim 1, further comprising: if an indicated available resource fromthe MAC entity is smaller than a size of one RLC STATUS PDU, skipping bythe RLC entity a transmission of the one RLC STATUS PDU for atransmitting opportunity.
 4. The method of claim 3, wherein theavailable resource and the one RLC STATUS PDU are checked for everytransmission time interval (TTI).
 5. The method of claim 1, furthercomprising: checking by the RLC entity for every transmission timeinterval (TTI) whether one of the RLC STATUS PDUs is scheduled fortransmission; and if one of the RLC STATUS PDUs is scheduled fortransmission, then informing a size of the corresponding RLC STATUS PDUto the MAC entity.
 6. A device configured to transmit radio link control(RLC) STATUS protocol data units (PDUs), the device comprising: a mediumaccess control (MAC) entity; and an RLC entity configured to: receive anindication of a total size of an RLC PDU from the MAC entity, prioritizea transmission of the RLC STATUS PDUs over RLC data PDUs, constructingthe prioritized RLC STATUS PDUs including a data/control (D/C) field, aCTP field, an ACK_SN field, and at least one NACK_SN field in order, theACK_SN field including current information that is not received, andtransmit the constructed RLC STATUS PDUs associated with the indicatedtotal size of the RLC PDU corresponding to a size of the RLC STATUS PDUsto a peer RLC entity, wherein the constructed and transmitted RLC STATUSPDUs include only negative acknowledgement information of RLC PDUs, andwherein the ACK SN field is for the peer RLC entity to indicate previousinformation that is received.
 7. The device of claim 6, wherein the RLCentity is configured to: perform a first step of allocating an availableresource to the RLC STATUS PDUs, and if any of the available resourceremains after the first step of allocating, then perform a second stepof allocating the remaining resource to the RLC data PDUs.
 8. The deviceof claim 6, wherein the RLC entity is configured to skip a transmissionof the one RLC STATUS PDU for a transmitting opportunity if an indicatedavailable resource from the MAC entity is smaller than a size of one RLCSTATUS PDU.
 9. The device of claim 8, wherein the available resource andthe one RLC STATUS PDU are checked for every transmission time interval(TTI).
 10. The device of claim 6, wherein the RLC entity is configuredto: check for every transmission time interval (TTI) whether one of theRLC STATUS PDUs is scheduled for transmission, and if one of the RLCSTATUS PDUs is scheduled for transmission, then inform a size of thecorresponding RLC STATUS PDU to the MAC entity.